Exothermic metal displacement reactions
Students add powdered or finely-divided metals to a copper(II) sulfate solution and measure the temperature rises. The experiment reinforces ideas about energy changes during reactions, the reactivity series of the metals and the chemical behaviour of metals.
The finely-divided metals should be distributed on labelled plastic weighing dishes or watch glasses to avoid cross-contamination and wastage.
Copper(II) sulfate(VI) solution, 1.0 M (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) 100 cm3
Powdered or finely–divided metals: iron, magnesium and zinc (HIGHLY FLAMMABLE), tin. Two spatula measures of each. (Note 3)
Refer to Health & Safety and Technical notes section below for additional information.
Each working group requires:
Expanded polystyrene cups standing in glass beakers for stability, 4 (Note 1)
Measuring cylinder (25 cm3)
Thermometer, -10 °C to +110 °C or similar
Large bowl or bucket for collecting the residues from experiments. Do not let students put residues into sinks. (Note 2)
Health & Safety and Technical notes
Wear eye protection.
Copper(II) sulfate(VI) solution, CuSO4(aq), (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSS Hazcard and CLEAPSS Recipe Book.
Powdered or finely divided metals: iron, Fe(s), magnesium, Mg(s), zinc, Zn(s), (all HIGHLY FLAMMABLE) and tin, Sn(s) - see CLEAPSS Hazcards.
1 A desirable, but not essential, addition are lids for the polystyrene cups. A lid can be made by cutting a suitably-sized piece from a polystyrene ceiling tile and making a hole for the thermometer.
2 Provide a bowl or bucket for discarding the residues. Metal residues in sinks are almost impossible to remove. Iron particles rust and cause unsightly stains.
3 Iron filings tend to be greasy and should be degreased using propanone (HIGHLY FLAMMABLE, IRRITANT, see CLEAPSS Hazcard) and dried before being used. Carry out degreasing in a fume cupboard.
a Measure 20 cm3 of the copper(II) sulfate(VI) solution into a polystyrene cup.
b Put the cup into a beaker so that it does not fall over.
c Measure and record the temperature of the solution.
d Add the first of the powdered metals and stir the mixture with the thermometer.
e Observe the temperature over the next few minutes until a maximum temperature is reached.
f Record the temperature rise.
g Repeat the procedure with fresh polystyrene cups using each of the other metals.
The temperature rises should be approximately:
- Magnesium 39°C
- Zinc 49°C
- Iron 32°C
- Tin 22°C
The results are approximately in line with the reactivity series of the metals. The ‘wrong’ order of magnesium and zinc might be due to oxidation on the surface of the magnesium being more extensive than for zinc.
Health & Safety checked February 2008
Page last updated on 30 December 2011